#16,092
As the SARS-CoV-2 virus spreads in humans, it continues to evolve, and while only a few variants exhibit enhanced transmissibility or biological fitness, they - by definition - have become more successful ones (e.g. D614G, Alpha, and Delta) around the globe.
Anecdotal reports now suggest Delta may be the most transmissible variant we've seen to date, with even brief exposures resulting in infection.
For the first half of 2020 the debate raged (see COVID-19: The Airborne Division) over whether COVID was transmitted via aerosols (as opposed to mainly short-range large droplets), and during the second half, evolved into `how much of a factor it was in the real world' (see Study: The Infectious Nature of Patient-Generated SARS-CoV-2 Aerosol).
While the first major change to the virus (D614G aka `the European Variant) appeared to increase the virus's transmissibility over the initial Asian strain (see Scripps Research Institute: SARS-CoV-2 and the D614G Mutation), it wasn't until the end of 2020 - after the emergence of the Alpha variant in the UK - that the alarm was truly raised.Until it was usurped by an even more transmissible variant (Delta), Alpha reigned as the most transmissible, and therefore successful, variant to date.
Despite these recent observations, the debate over the importance of small (<5 µm) aerosol particles in the spread of COVID continues. The concern being that smaller particles may remain aloft longer, travel farther, and be drawn deeper into the respiratory tract, possibly resulting in more severe illness.
While obviously of academic interest, better answers could help drive more effective PPE (Personal Protective Equipment) recommendations, and improved definitions for what constitutes `close contact' with an infected patient.
Today we've got a preprint from researchers at the NIH, which takes the closest look yet at the aerosol transmission of the older (Lineage A) COVID variant vs the Alpha variant in the Syrian Hamster model.
This study not only confirms efficient transmission by aerosol particles <5 µm by both variants, it also found that that the Alpha variant showed a transmission advantage over the older lineage in a dual infection experiment.
I've only reproduced the Abstract below (bolding mine), so you will want to download and read the full (49-page) PDF. I'll have a brief postscript when you return.
Julia R. Port, Claude Kwe Yinda, Victoria A. Avanzato, Jonathan E. Schulz, Myndi G. Holbrook, Neeltje van Doremalen, Carl Shaia, Robert J. Fischer, Vincent J. Munsterdoi: https://doi.org/10.1101/2021.07.26.453518This article is a preprint and has not been certified by peer review [what does this mean?].0000363AbstractAirborne transmission, a term combining both large droplet and aerosol transmission, is thought to be the main transmission route of SARS-CoV-2. Here we investigated the relative efficiency of aerosol transmission of two variants of SARS-CoV-2, B.1.1.7 (alpha) and lineage A, in the Syrian hamster.A novel transmission caging setup was designed and validated, which allowed the assessment of transmission efficiency at various distances. At 2 meters distance, only particles <5 µm traversed between cages.In this setup, aerosol transmission was confirmed in 8 out of 8 (N = 4 for each variant) sentinels after 24 hours of exposure as demonstrated by respiratory shedding and seroconversion. Successful transmission occurred even when exposure time was limited to one hour, highlighting the efficiency of this transmission route.Interestingly, the B.1.1.7 variant outcompeted the lineage A variant in an airborne transmission chain after mixed infection of donors. Combined, this data indicates that the infectious dose of B.1.1.7 required for successful transmission may be lower than that of lineage A virus.The experimental proof for true aerosol transmission and the increase in the aerosol transmission potential of B.1.1.7 underscore the continuous need for assessment of novel variants and the development or preemptive transmission mitigation strategies.
By some accounts, the Delta variant may be twice as transmissible as the Alpha variant, which would explain why Delta has supplanted Alpha so quickly in the the UK, Europe, and the United States.
Presumably an Alpha vs. Delta version of this experiment is in the works.
Until those results are in, we have to base our decisions on admittedly less scientific observational data, and that strongly suggests that we need to up our game if we hope to avoid another bad wave of COVID this fall and winter.
No one likes to wear masks, social distancing, or having to get vaccinated - but those are the only tools we have.
